Generally, a the car body is conveyed to each of several assembly lines by an overhead hanger that is connected to the ceiling, while a worker fastens components at the bottom of the car body. As for the process of fastening various kinds of arms to a suspension system of a car, a worker grips a manual torque wrench, and works below the car body, looking up a fastening part of arms located above the worker. In a rear wheel suspension system, a fastening torque of a nut regulating a toe and camber has a range of only 11 to 12 kgfm, which may cause harm to muscles and bones of workers.